1. Field of the Invention
The invention in general relates to sonar apparatus, and particularly to a system which is able to detect a target and classify targets as being moored above the sea bottom or lying on it.
2. Description of the Prior Art
Detection of an object, stationary in, or moving through, the water column involves the projection of acoustic energy toward the area under investigation. An object in the area will cause a distinctive detectable return of a magnitude much higher than any reverberation which may be caused by particulate matter in the water, and accordingly is detectable. Detection and classification of objects near the sea .bottom, however, is more difficult because the return from the bottom itself is nearly equal in magnitude to the return from the objects themselves.
Established systems for detecting such near bottom targets require the formation of extremely narrow beams so that the shape or shadow of the object can be used in detection and classification. The formation of such narrow beams generally requires an elongated transducer arrangement which, for some underwater carriers, becomes impractical.
Although narrow beams may be utilized in the improved technique of the present invention, they are not an absolute requirement.